Charge/discharge protection circuit for a rechargeable battery

• US 6,710,992 B2
• Filed: 01/24/2002
• Issued: 03/23/2004
• Est. Priority Date: 01/25/2001
• Status: Expired due to Term

• Current Assignee: Dialog Semiconductor GmbH (Renesas Electronics Corporation)
• Original Assignee: Dialog Semiconductor GmbH (Renesas Electronics Corporation)
• Inventors: von Staudt, Hans Martin, Stellberger, Achim, Pannwitz, Axel
• Primary Examiner(s): Patel, Rajnikant B.
• Application Number:
  US10/057,490
• Publication Number:
  US 20020097543A1
• Time in Patent Office: 789 Days
• Field of Search: 361/90, 361/92, 361/93.2, 361/93.4, 361/104, 320/134, 320/152, 320/154, 320/163, 320/164
• US Class Current: 361/90
• CPC Class Codes: H02J 7/00302 Overcharge protection
• CPC Class Codes: H02J 7/00306 Overdischarge protection
• CPC Class Codes: H02J 7/00308 Overvoltage protection
• CPC Class Codes: H02J 7/0031 using battery or load disconnect circuits H02J9/002 takes precedence

Abstract

The invention refers to a charge/discharge protection circuit for a rechargeable battery which is protected by a fusible link, where the rechargeable battery comprises a control logic which opens or closes a load switch depending on the magnitude of the battery voltage, the voltage on the charge/discharge terminals of the protection circuit and the charge/discharge current. The protection circuit is designed so that the electric strength needs to match only the actual maximum battery voltage, thus requiring little real estate on an IC chip and also allowing most components to be integrated.

Claims

1. A charge/discharge protection circuit for a rechargeable battery, comprising:

a short-circuit switch coupled in series with a fusible link across the terminals of a rechargeable battery, where one end of said fusible link is connected to one of said battery terminals, where said short-circuit switch when closed leads to the guarantied destruction of said fusible link, thereby protecting said rechargeable battery from a dangerous current over-charge;

one end of a load current switch coupled to the junction of said fusible link and said short-circuit switch, the other end of said load current switch in communication with a first charge/discharge terminal of said protection circuit, said load current switch connecting or disconnecting said first charge/discharge terminal from said rechargeable battery;

a second charge/discharge terminal of said protection circuit coupled to the other end of said battery terminal;

a control logic, coupled between said battery terminals and in communication with said first charge/discharge terminal, said control logic protecting said battery and said first and said second charge/discharge terminal from over-/under-voltage conditions, where said control logic opens or closes said load current switch depending on the magnitude of the battery voltage and the potential at said first and said second charge/discharge terminal of said protection circuit, said control logic comprising an over-voltage detector which closes said short-circuit switch when reaching a predetermined voltage limit, where said predetermined voltage limit depends on the electric strength of said protection circuit; and

where with the exception of capacitors, all parts of said protection circuit are integrated on said chip, including said load current switch, said short-circuit switch, and said fusible link.

2. The protection circuit according to claim 1, wherein said over-voltage detector receives as input voltage the potential via the opened load-current switch.

3. The protection circuit according to claim 2, wherein said over-voltage detector receives as input voltage the difference between the potential at said first and said second charge/discharge terminal and the potential at said battery terminals.

4. The protection circuit according to claim 3, wherein, when said predetermined voltage limit is exceeded, said control logic closes the previously open load-current switch followed by the time-delayed closing of said short-circuit switch.

5. The protection circuit according to claim 4, wherein said control logic receives a first supply voltage from said battery and a second supply voltage from an auxiliary voltage source, such as a charged buffer capacitor.

6. The protection circuit according to claim 1, wherein said over-voltage detector comprises a bistable flip-flop.

7. The protection circuit according to claim 6, wherein an output signal of said bistable flip-flop feeds a delay-element, said delay-element providing the control signal for the closing of said short-circuit switch.

8. The protection circuit according to claim 7, wherein said output signal of said bistable flip-flop via an inverter couples to the first input of an AND gate, where the output signal of said AND gate controls said load-current switch.

9. The protection circuit according to claim 1, wherein a resistive means in communication with said other end of said current-load switch and said first charge/discharge terminal acts as a current sensor to determine the magnitude of the charge or discharge current.

10. The protection circuit according to claim 1, wherein the transmission resistance of the said load-current switch is used as a current sensing resistance.

11. The protection circuit according to claim 1, wherein said control logic has a first and a second comparator (Dl, D2), to recognize a battery-side over-/under-voltage, respectively.

12. The protection circuit according to claim 11, wherein an output signal from each of said first and said second comparator triggers the opening of said load switch in the event of an over-/under-voltage, respectively.

13. The protection circuit according to claim 1, wherein a filter capacitor is coupled parallel to said charge/discharge terminals.